The present invention relates to an arrangement for the sensing of the material thickness on a roll of weblike material.
Weblike material is used very widely in various branches of industry. In the technique of packaging, for example, flexible weblike material is used as a starting material in the manufacture of packages, packing containers or the like. The conversion of the weblike material to finished packages takes place in packing machines which have a magazine to accommodate the web-like material in rolled-up condition. During operation of the machines the roll of weblike material is successively used up and has to be replaced, therefore, at regular intervals. To assist the machine operator, as he occasionally may have to handle several machines, the packing machines are generally provided with some form of indicating arrangement which visually or acoustically gives a signal when a roll diameter has been reduced to such an extent that roll replacement is imminent.
Known arrangements for the sensing of the material thickness on a roll of weblike material are usually either of the mechanical or of the optical type. The mechanical arrangements generally make use of an arm resting against the roll periphery which as it approaches the roll centre, as the material is being used up or depleted, acts upon a limit switch to transmit an electric signal to an indicating arrangement. The optical type operates with a photocell which is located on one side of the material roll and which, after a certain consumption of material, is struck by a light beam from a light source situated on the opposite side of the roll. At this the photocell transmits a signal to an indicating arrangement of the known type.
Both these known arrangements have proved to function well and provide a relatively reliable indication, so that the web splicing and the roll replacement can be done in good time and without the loss of an excessive quantity of residual material on the roll. The satisfactory operation fully depends, however, on the roll centre being in a fixed position in relation to the sensing element during the whole time of the material consumption. This condition can be achieved only if, in the first place, the axle which supports the material roll is rotatable in fixed bearing points on the frame of the machine and, in the second place, the outside diameter of the axle (possibly with intermediate elements, e.g. flanges or the like) corresponds to the inside diameter in the bobbin upon which the material is rolled up. The design and function of the sensing arrangement thus make demands on the suspension of the material roll which, otherwise, are not required, and it would be desirable, therefore, to provide a sensing arrangement which could operate with sufficient accuracy even on loosely suspended, radially movable material rolls.
It is an object of the present invention to provide an arrangement for the sensing of the material thickness on a roll of weblike material, with the arrangement not subject to the disadvantages of earlier, similar arrangements. The present invention allowing a reading of the material thickness on a roll even if it is moved in an irregular manner in a radial direction during the consumption of material.
It is a further object of the present invention to provide a sensing arrangement of the aforementioned type which is simple to manufacture and inexpensive and which gives such accuracy that the material wastage can be minimized.
These and other objects have been achieved in accordance with the invention in that an arrangement of the type described provides a movable sensing device resting against the periphery of the roll and adapted so that at a predetermined distance from the centre of the roll it is acted upon by a field-generating element located in the central part of the roll.
Owing to the sensing device present on the periphery of the roll being adapted to be acted on at a certain distance from the centre of the roll by a field-generating element present in the central part of the roll, the residual material thickness between the sensing device and field-generating element only will be registered. Any movements in the roll in radial direction will not affect the sensing device, since movements of the roll with respect to the point of suspension of the material roll have no consequence. Thus the material roll can be suspended in a very simple and labor-saving manner, e.g., an under-dimensioned axle is stuck through the bobbin of the roll and subsequently is placed freely movable between two V-shaped bearing elements.
A preferred embodiment of the arrangement in accordance with the invention will now be described in detail with special reference to the enclosed schematic drawing which only shows the parts indispensable for the understanding of the invention.